The invention relates to a cutting tool, in particular a contour milling cutter for machining printed circuit boards or the like having a cutting part with staggered teeth, the staggered teeth being defined by main cutting grooves which are intersected by a plurality of divider grooves.
Contour milling cutters have been disclosed for the machining of in particular glass-fiber reinforced printed circuit boards, said contour milling cutters generally consisting of solid carbide material having a pyramid-like tooth shape and a diameter of 0.4 to 3 mm. The period of use or the useful length of the tool is essentially determined by the nature of the material to be machined and by the cutting-edge geometry of the individual cutting edges of the milling cutter. For the cutting-edge geometry, a so-called staggered toothing or also diamond toothing is employed. For this purpose, the tool is provided with a particular number of main cutting grooves having main cutting edges with a particular lead which are intersected by a particular number of divider grooves or secondary cutting grooves having an opposing lead. The main cutting grooves are divided by the divider grooves into subregions, so that each initially continuous main cutting edge is divided by the divider grooves into a multiplicity of individual cutting elements of small width. This is necessary in order to reduce the stressing of the cutting edge and the heating up of the contour milling cutter in order to decrease the risk of breakage.
Hitherto, the following criteria have been considered in the production of the staggered toothing consisting of main cutting grooves and opposing divider grooves. If the number and lead angle of main cutting grooves and divider grooves are chosen to be the same, axial gaps which have no cutting tooth are produced. Therefore this method is generally unsuitable for the production of staggered toothing.
In order to avoid obtaining axial gaps in the cutting zone, one method of producing staggered toothings provides that the number of main cutting grooves is chosen to be different from the number of divider grooves while the lead angle of both groove types remains the same. If, for example, a difference of "1" between the number of main cutting grooves and divider grooves is chosen, for example seven main cutting grooves and eight divider grooves while the lead remains the same, one individual cutting element is obtained at one axial level, i.e. in one radial plane on the entire periphery, which is succeeded, as seen axially, by a further individual cutting element which is offset by a particular angle on the periphery, no overlap of the cutting teeth occurring in the axial direction.
If a difference of "2" between the number of main cutting grooves and divider grooves is chosen, e.g. eight main cutting grooves and ten divider grooves, this produces a milling tool in which two individual cutting elements are arranged offset by a particular angle at one axial level, i.e. in one radial plane. Here too, the further cutting elements arranged in a different axial position merely succeed one another without an axial overlap of individual cutting elements occurring. A development of the cutting shell of such a contour milling cutter is shown in FIG. 5. In this arrangement, eight main cutting grooves and ten divider grooves have been chosen. The vertical dashed region indicates the respective subregion of the start and end of two axially successive teeth with direct corner succession. This is described in greater detail below.
If an equal number of main cutting grooves and divider grooves is chosen in combination with different lead angles of the two groove types, this does give a multiplicity of cutting elements at one particular axial level, i.e. in a particular radial plane, said cutting elements being arranged offset with respect to one another in accordance with the magnitude of the lead differences. However, a multiplicity of cutting elements arranged in the same radial plane increases the frictional forces and reduces the cutting pressure on the individual cutting tooth or individual cutting element. This production method is therefore also unsatisfactory.